The broad aim of this project is to investigate the effects of aging (old age) on the mitochondrial metabolism in the mammalian brain. This investigation will center around two major areas: the effect of aging on (1) the mitochondrial oxidative (energy) metabolism in the brain, and (2) the metabolic compartmentation of dicarboxylic amino acids in the brain. The oxidative metabolism both in vivo and in vitro of glucose and ketone bodies by brains of 2 months, 1 year and 2 year old male rats will be studied using the arterial-venous difference across the brain (in vivo studies) and the oxidation of labeled substrates by cerebral cortex slices (in vitro studies). To delineate possible metabolic alterations in the brain due to aging, mitochondrial respiration studies, levels of the TCA cycle enzymes, pyruvate and ketone bodies-utilizing enzymes and the steady state levels of adenine nucleotides and other metabolites in the brain will be investigated. For the latter studies, the brain will be frozen in situ by the brain-blowing technique. The mitochondria localized in two anatomically defined compartments (neuronal and glial cell bodies vs nerve endings) will be separated using discontinuous sucrose and Ficoll-sucrose gradients, osmotic shock treatment to synaptosomes and differential centrifugations. The effect of aging on metabolic capacities of these two mitochondrial populations will be investigated. To study the effect of aging on the metabolic compartmentation of amino acids in the brain, the steady state levels of dicarboxylic amino acids as well as the incorporation of several labeled compounds into these amino acids in vitro will be investigated.